This document discusses Android Pie UI design. It provides an overview of Android design history from Cupcake to Pie. It then discusses four key aspects of Android Pie UI design: 1) It uses Google's original Material Theme, 2) It utilizes a bottom app bar and bottom sheets instead of an app bar and hamburger menu, 3) It has a new navigational hierarchy with more simplified and subtle elements, and 4) It supports dark themes. Examples of apps that follow the Android Pie design are also presented.